After he finished this film, Martin Scorsese screened the film for John Cassavetes. Cassavetes, after seeing this film, hugged Scorsese and said, "Marty, you've just spent a whole year of your life making a piece of shit. It's a good picture, but you're better than the people who make this kind of movie. Don't get hooked into the exploitation market, just try and do something different." Scorsese's next film was Mean Streets (1973).
The rumor that Roger Corman's wife Julie obtained the film rights to the story from Bertha Thompson herself who she tracked down in a San Francisco hotel room but never actually met since she wouldn't open the door turns out to be untrue (but possibly a pre-release publicity stunt or maybe even a trick played on the Cormans by the true owner of the story, the author Ben Reitman), as the afterward in the fourth re-issue of the book Boxcar Bertha explained that the book is a work of fiction, and that the character Bertha Thompson was an amalgam of at least three women that the author (Ben Reitman) knew, but was mostly modeled on a woman named Retta Toble.
The Reader Railroad was the actual name of the railroad where the train scenes were filmed. It opened in 1889 and is still in business, used at various times for freight, tourism, and movie service. At the time of filming, it was still regularly using vintage equipment, most notably steam locomotives.
There are no characters in the film named Emeric Pressburger or M. Powell, and there are no such actors as Grahame Pratt or "Chicken" Holleman. Martin Scorsese added them to the cast list as a tribute to Michael Powell and Emeric Pressburger.